Disc screw extruders are in common use for processing a wide variety of materials, most typically synthetic resinous materials but also including food products, waste products, and the like. The screw component of the operating members of such machines serve to advance the charge of material to the disc component, where it is subjected to shear forces; the magnitude of the forces generated depend, to large measure, upon the dimensions and configuration of the flow paths formed between the confronting surfaces of the disc and the extruder body.
The prior art provides disc screw extruders in which the axial position of the operating member can be adjusted for variation of the effective size of the extrusion gap. Extruders are also known in which the operating member effects axial reciprocation as well as rotation, for enhanced working of the processed material.
Exemplary of prior art in this field are the following: French patent No. 1,559,634 provides an extruder in which the gap between the disc of the operating member and the adjacent, cavity-defining plate increases in a radially inward direction, while its flow cross section is maintained constant or diminishes slightly, so as to afford desirable levels of plasticization without overheating of the material. A disc screw extruder is disclosed in French patent application No. 2,204,495, in which the operating member is movable on its axis of rotation for effecting injection of the melt into an associated mold. Japanese patent publication No. 55-36497 provides a dual-effect symmetric extruder in which opposing screw components lead to the opposite sides of a common disc.